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Cristina Flox¹, Fatemeh Davodi¹, Davide Pavesi^2,3 and Tanja Kallio¹

1 – Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, FI-00076, Espoo, Finland

2 – Avantium Chemicals BV, Zekeringstraat 29 1014 BV Amsterdam, The Netherlands

3 – Leiden Institute of Chemistry, Leiden University, PO Box 9502, 2300 RA, Leiden, The Netherlands

cristina.flox@aalto.fi

Electrochemical CO₂ reduction reaction is a key technology for the mitigation of the climate change. However, CO₂ reduction is highly energetic and unfavourable electrochemical reaction, requiring catalyst to achieve economically appealing performance. In this scenario, Nickel-Nitrogen (Ni-N)-active sites within porous carbon are attracting increasing interest as inexpensive and efficient electrocatalyst of CO₂ reduction. In fact, the Ni-N- active sites anchored to the carbon structures have been proposed as excellent solution for the conversion CO₂-to-CO, exceeding selectivity and partial current density values of the commercial electrocatalyst. Herein, the in-situ creation of Ni-N-active sites using Nickel Carbide nanoparticles-wrapped in a graphene shell (Ni₃C@graphene NPs) and Emeraldine as precursors in combination with the thermal treatments is evaluated. As a result, the Ni-N- active sites in combination with Ni₃C@graphene NPs provide a new paradigm, where the formate production is dominated leading a complete deactivation of CO route. Surprisingly, the unprecedent key performance indicators of the CO₂ reduction showed a Faradaic Efficiency up to 90 % at 0.55V vs. RHE at 25ºC. Additionally, the CO₂-to-formate conversion showed a temperature sensitive- dependence, increasing the selectivity (up to 96 %) in the voltage range tested (0.45 to 0.7V vs. RHE), when the electrolysis was performed at 40ºC. The apparent Energy Activation values were calculated, attaining values up to 45 kJ mol^-1 at -0.55 V vs. RHE@40ºC, which agrees well with previous reports. Therefore, the creation of Ni-N- active sites in the Ni₃C@graphene NPs can effectively reduce the energy barrier towards the CO₂-to formate conversion, providing new mechanism insight for the CO₂ reduction.

Cristina Flox received her PhD in Electrochemistry applied to flow reactors from Universitat de Barcelona in 2008, followed by postdoctoral fellowships in LEITAT and Catalonia Institute for Energy Research, Spain (2008–2017). Subsequently, she joined Aalto University in 2017, working on the design of innovative nanomaterials for energy applications. Particularly, she is focused on the development of electrodes for CO₂ reduction and solid-electrolytes for lithium-ion batteries. Additionally, her research interest are fundamental aspects on energy storage systems, especially redox/semi-solid flow batteries, supercapacitors and Na-ion batteries. She published more than 47 refereed articles (h index 23, 2025 citations), 3 book chapters and 1 patent application.